The present invention generally relates to the production of hydrocarbon fluids from a subterranean formation, and, more specifically, to the use of relative permeability modifiers in conjunction with the production of hydrocarbon fluids.
Water can often undesirably accompany the production of hydrocarbons from a well penetrating a subterranean formation. In a subterranean formation, water's high mobility can often allow it to flow to or from a wellbore by way of natural and manmade fractures, highly permeable zones, and the like. The unwanted production of water from a hydrocarbon-producing well can constitute a considerable technical problem and expense in oilfield operations. If the ratio of produced water to produced hydrocarbons becomes sufficiently large, the cost of separating the water and disposing and/or treating it can become a significant issue. For example, in some instances, poor well economics arising from excess water production can lead to abandonment of a wellbore, even when significant amounts of hydrocarbons remain within a subterranean formation penetrated by the wellbore.
One way in which the production of water from water-producing subterranean zones has been addressed is through the use of relative permeability modifiers (RPMs). RPMs may reduce the production of water from a subterranean zone without substantially reducing the production of hydrocarbons therefrom. Thus, RPMs may slow the production of water from the subterranean formation and make a well more economically feasible to produce. An advantage of RPMs over other techniques for reducing water flow in a subterranean formation is that RPMs usually do not necessitate the use of zonal isolation techniques to successfully place the treatment in a desired location, since reduced hydrocarbon production is generally not a concern with their use.
Although RPMs may slow the production of water from a subterranean formation, water production may sometimes still be unacceptably high after treatment. In these instances and others, instead of an RPM, a sealant composition may be introduced to a water-producing zone to at least partially block the flow of fluids therefrom. Unlike RPMs, which only significantly impede the production of water, sealant compositions may impede the production of all fluid types by forming an impermeable fluid seal. Sealant compositions may comprise, for example, water-soluble, gellable polymers that can enter a water-producing subterranean zone, where they subsequently gel to form a fluid seal that impedes fluid flow. Other sealant compositions are known and may function in a similar or related manner. In contrast to RPMs, zonal isolation techniques may sometimes be needed when using a sealant composition to prevent its incursion into a hydrocarbon-producing subterranean zone, where it may produce damage that reduces hydrocarbon production.
Although zonal isolation techniques may oftentimes be sufficient to place a sealant composition in a desired location (e.g., a water-producing subterranean zone), in some instances a sealant composition may still enter an undesired location (e.g., a hydrocarbon-producing subterranean zone). Reasons why a sealant composition might undesirably enter a hydrocarbon-producing zone may include, for example, failed zonal isolation strategies or fluid conduits (e.g., natural or manmade fractures, or like means of fluid communication) extending between the hydrocarbon-producing zone and the water-producing zone that are not easily addressed by zonal isolation techniques. Migration of a sealant composition from a water-producing zone to a hydrocarbon-producing zone may be especially problematic when the hydrocarbon-producing zone and the water-producing zone are located close to one another in the subterranean formation. In some instances, there may be no natural subterranean barrier existing between the hydrocarbon-producing zone and the water-producing zone to prevent fluid exchange therebetween. In such cases, a sealant composition, even if properly diverted to a water-producing zone, may undesirably impact production from the hydrocarbon-producing zone. In such cases, remediation operations may sometimes be needed to return the wellbore to production. In more extreme cases, if the hydrocarbon-producing zone cannot be remediated, the wellbore may have to be abandoned.
One way in which a sealant composition may be at least partially prevented from entering a hydrocarbon-producing zone from a neighboring water-producing zone is to introduce the sealant composition at low pump rates so as not to promote an overpressure that forces the sealant composition into the hydrocarbon-producing zone. Another way this problem can be solved is to introduce a non-damaging fluid into the hydrocarbon-producing zone at the same time as a sealant composition is being introduced to the water-producing zone. The non-damaging fluid may exert sufficient outward pressure within the hydrocarbon-producing zone to at least partially prevent the inward incursion of the sealant composition from the water-producing zone. Either of these treatment protocols may significantly increase the complexity and cost of hydrocarbon production, and they may oftentimes only provide a limited degree of success in preventing incursion of a sealant composition into the hydrocarbon-producing subterranean zone.